1. Field of the Invention
The present invention relates to compositions useful, for example, in water-based paints. The compositions contain a moisture sensitive luminescent substance (for example a phosphorescent substance having increased brightness and longer lasting afterglow) and a polyurethane resin which is water miscible or soluble, and which imparts moisture stability to the luminescent substance. As a result, the composition when used in water-based paints imparts an extended road surface life, and is environmentally friendly because it does not contaminate the surrounding environment with organic hydrocarbon products via vaporization or runoffs. In addition this paint composition may be used both indoors and outdoors for nighttime marking.
2. Background Art
It is presently desirable to produce indoor and outdoor luminescent paints whose compositions do not require organic solvents whose vapors are undesirable when released into the atmosphere and contaminate the surrounding soil or land near roadway surfaces via runoffs. U.S. Pat. No. 4,172,063 discloses an abrasion resistant reflective marking composition containing cement, a fluorescent pigment, silica, glass fibers and a timing bonding acrylic polymer agent. This composition is, however, not environmentally friendly nor does it exhibit any sustained lasting afterglow or extended durability or weatherability.
The term "luminescence" as used in this specification and in the appended claims is meant to be that property of a material which causes visible light to be continued to be emitted after an exciting light source has been removed as well as that property of a material to glow under a source of light of low visibility and suitable wavelength. U.S. Pat. Nos. 223,050; 274,415; 1,407,534 and 1,637,963 disclose the use of luminous (phosphorescent) compositions in paint, enamels, and as a coloring in paper. These luminous or phosphorescent materials exhibit reduced or degraded light resistance over time. A paint mixture with an acrylic vehicle but having an alkaline earth phosphor other than zinc sulfide, which could be modified by replacing its alkaline earth phosphor with zinc sulfide to obtain a preferred phosphorescent paint is described in U.S. Pat. No. 2,436,182. All of these cited references are incorporated in their entirety herein.
As is well-known, fluorescent paints when excited by a source of light produce an emission of light but the light emission is limited to the period of excitation. Such paints can be selected to provide a day time coloration which will demarcate and emphasize areas to be marked such as edges of steps, corners of walls, highway edges and median traffic divider stripes.
Phosphorescent paints on the other hand, once they have been excited, remain luminous with a soft, slowly decaying emission or radiation. Such phosphorescent paints can generate a useful level of luminous flux for periods of time (even several hours) after being activated when exposed to sunlight or artificial light (such as from headlights of automobiles) in the dark of night. After an initial exposure to a light source, luminescence can be renewed by once again exposing the paints to either a natural or an artificial light. Thus, highway paints have incorporated fluorescent or phosphorescent substances to demarcate the edges of highways and the median line of the highway to differentiate the different directions of the highway vehicles. Previously phosphorescent containing highway paints tended to lose their luminescence through chemical attack by the atmosphere (ultraviolet radiation and/or presence of moisture) on the phosphor. In such outdoor uses, the luminescent paint compositions lost most of their phosphorescence capacity in a matter of days.
U.S. Pat. No. 5,424,006 disclosures phosphorescent phosphors which can be utilized both indoors and outdoors as a nighttime display and show extremely long afterglow characteristics. However, these phosphorescent phosphors must be incorporated into chemical hydrocarbon solvent based systems as they are adversely affected by moisture or aqueous systems. This reference is incorporated by reference in its entirety.
Luminescent (phosphorescent) highway paint compositions should have the following characteristics: ease of application, short track time, long wearability, moisture stable (insensitive) luminescent pigment and suitably long duration of afterglow luminescence. Of these, the most difficult to achieve is long wearability under normal traffic conditions and long duration of afterglow luminescence. Accordingly, it is a principal object of the present invention to provide a composition suitable for use in highway or roadway paint that is environmentally protective, exhibits long duration afterglow luminescence and has increased roadway life and durability, and is stable to the detrimental effects of moisture as well as ultraviolet radiation.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description of the invention.